A mixing instrument of this type has become known through the German patent 11 22 355.
Mixers having horizontal containers are known for the mixing of pourable materials, in which the material to be mixed is moved with a mixing instrument rotating with the shaft. Plough-share blades are preferentially utilized as mixing instruments and have proven themselves over a wide range of applications. With these mixing instruments it is possible to produce multicomponent mixtures of high mixing quality. Plate-shaped mixing bodies are also known which exhibit sectional areas which are concave and/or convex. Should strongly adhering products be mixed, dried or processed in some other fashion in horizontally arranged mixers, driers or reactors it is known that a product layer can build-up on the inner wall of the container, forming between the inner wall of the container and the front surface of the mixing element (product deposit).
An increased gap between the mixing instrument and the inside wall of the container occurs because the shaft, due to its own weight, exhibits a certain amount of bending if it is rotatably mounted only at the shaft ends. In addition an increased gap between the mixing instrument and the inner wall of the container is also required when the container wall is warmed by means of an energy carrier. The container thereby experiences a certain deformation which changes in dependence on the temperature and the material utilized for the container, the shaft and/or the mixing instrument. It is therefore clear, even in highly precise manufacturing of mixers, driers, and reactors, why an increased gap between the mixing instrument and the inner wall of the container is necessary.
The product deposit which builds up in the gap can harden and continue to build-up so that the energy absorption of the mixing instrument is increased. The deposit can break-off from time to time and thereby, cause a deterioration of the quality of the final mixture. A product deposit of this kind is also overheated in driers or reactors, so that the product itself is destroyed in the vicinity of the inner walls of the container. In reaction processes stoichiometric conditions could thereby change in an uncontrolled fashion.
The known mixing instrument is for these reasons secured in the product region, in a resilient fashion, in order to adjust, by means of a predetermined spring tension, the gap width between the inner wall of the container and the front surface of the mixing instrument. This causes difficulties in construction and is suspectible to failure during manufacturing operations.
A cleaning device for mixing containers or for containers capable of performing motion is known from U.S. Pat. No. 2,320,976 which comprises harrow-like flexible blades. The blades are displaced and attached to rods which move the material to be mixed. The rods rotate and the blades seat, under bias, on the inside surface of the container and thereby scrape product deposit off the inside wall. The blades are seated in a pivotable fashion.
The underlying purpose of the invention is therefore to further improve a mixing instrument of the above mentioned kind in such a manner that the product deposit in the gap between the inner wall of the container and the mixing instrument is largely prevented or is removable in a reliable fashion.
This purpose is achieved in accordance with the invention in that the mixing elements are arranged at least partially behind one another in the circulating direction and exhibit openings on the free end facing the inner wall of the container which are displaced between the first mixing element and the second mixing element and in that the openings, as viewed from the front, are at least partially covered by projections of the second mixing element. The mixing instrument in accordance with the invention thereby has the essential advantage that it allows for the removal of product deposits, built-up in the gap, in narrow paths. The power consumption of the shaft which supports the mixing instruments can be kept small. One projection, adjacent to the openings, is provided for between each individual opening. By means of these projections the product deposit is torn open along a certain axial length. The product deposit strips which still remain are then removed from the projections of the second mixing element. The projections which are arranged, displaced with respect to each other, on the mixing element guarantee that the entire inner wall of the container in the vicinity of the plane of rotation of a mixing instrument is covered so that residual circular-shaped product deposit rings cannot occur. Furthermore, the individual mixing instruments work together in such a manner that the entire axial length of the inner wall of the container is covered. In this fashion, using a simple configuration of the mixing elements on the mixing instrument, the build-up of product deposit is largely prevented and product deposits which occur are easily removed with small expenditures of energy. The wear or abrasion associated with this type of mixing element is reduced.
The individual mixing elements are, in the event of hard product deposits, furthermore subjected to reduced moments and can therefore be produced from materials of reduced strength.
By means of the orbit-shaped removal of the product deposit it is also possible to loosen the longitudinal edges of the product deposit paths in such a manner that it is easier to remove these product deposit tracks from the inner wall of the container by means of the projections of the second mixing element.
In a preferred configuration of the invention a front surface of the mixing element facing the inner wall of the container forms a wedge-shaped gap with the inner container wall. Thereby, as seen in the direction of rotation of the mixing instrument, the rear edge of the mixing element exhibits a larger separation from the inner wall of the container than that of the forward edge. This has the advantage that, depending on the specific behaviour of the product deposit of a given product, an increased or decreased free angle between the mixing instrument and the inner wall of the container can be adjusted. The wedge angle opens oppositely with respect to the rotational direction of the mixing instrument so that no pressing of the loosened product deposit can transpire between the inner wall of the container and the mixing instrument. The energy absorption of the shaft can thereby be kept low.
If, furthermore, the mixing elements exhibit varying distances from the inner wall of the container, it is possible to a greater extent, to take into consideration the specific behaviour of a given product deposit.
In a preferred embodiment, the mixing elements are arranged diagonally with respect to the arm of the mixing instrument in the rotational plane of the mixing instrument so that a defined transporting of the product to be handled in the container can take place. The product exchange in the container and thereby the mixing quality or the yield can be improved with a mixing element configuration of this type.
The projections of the second mixing element are formed in such a manner that they describe the same path of travel as the openings of the first mixing element. The first projections of the first mixing elements stand in similar relationship to the second openings of the second mixing element. If the mixing elements are directed differently, e.g. if the mixing elements do not run precisely parallelly behind another, it is necessary to adjust the openings of the first mixing element to the projections of the second mixing element in such a fashion that they describe the same path of travel on an inside wall of the container.
The mixing instrument in accordance with the invention thereby observes the extensive requirements of mixing technology. With the trailing mixing element it is possible to effect an additional backward mixing and thereby an improved homogeneity of the final product. The energy requirement is reduced compared to conventional mixing elements. This is due to effects which are, per se, known. The emptying out of the product is improved and the granulating characteristics of the inventive mixing instrument are better than those of the known mixing instruments of prior art. Through the change of the angular orientation of the mixing elements with respect to each other, the change of the angle of the leading mixing element, as well as the angle of the mixing elements with respect to the inner wall of the container, a product specific adjustment of the mixing instrument is possible.
Further advantages are derivable from of the description and the accompanying drawing. The previously mentioned characteristics of the invention and those which will be described below can, likewise, each be used individually or with another in arbitrary collective combination. The embodiments mentioned are not to be considered as exhaustive enumeration, rather have only exemplary character.